System Modeling ESD.864 Noelle Selin March 19, 2013

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Plan for Today

Reminders/Q&A System Modeling Last 15 minutes: Forum Discussion

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Outline

System modeling: an introduction Box Modeling Principles Modeling in Engineering Systems Modeling in Context Analysis Techniques Application: Chemical box model

(prep for PS 4)

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Basic Modeling

Many classes of models (e.g. system dynamics, stock-flow, complex climate models) are extensions of the “box model” concept Including many we’ve seen in case

studies Key concepts: mass balance and

lifetime

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One-Box Model spatial distribution of X within box is not

production loss resolved

Inflow Fin X

Outflow FP L out

D E

“Deposition” “Emission”

dmMass balance equation: = ∑ ∑sources - sinks = Fn E Fout L Ddt i + + P − − −

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Box model intuition quiz

The lifetime of X in the box depends on which of the following: A) inflow, production, and emission B) outflow, deposition and loss C) amount of X in the box D) all of the above

Assume first-order loss rates.

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Constant source, 1st order sink

dm ( ) (0) kt S= S − km ⇒ m t = m e− + (1− e−kt )

dt k

© Princeton University Press. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/.Source: Figure 3-2 in Jacob, Daniel. Introduction to Atmospheric Chemistry. Princeton University Press, 1999.

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Two-box model F12

m1 m2 F21

dm1Mass balance equations: = E1 + P L1 − 1 − D1 − F +dt 12 F21

(similar equation for dm2/dt)

If mass exchange between boxes is first-order:

dm1 = E1 + P1 − L1 − D1 − k12m1 + k21mdt 2

system of two coupled ODEs (or algebraic equations if system is assumed to be at steady state)

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Modeling in engineering systems

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Modeling and user understanding

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Analysis Techniques

Sensitivity analysis Uncertainty analysis (Monte Carlo)

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Chemical Box Model: The OECD Screening Tool (PS 3)

Single region Global dimensions Air, water, soil

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POPs: Specific category of particularly hazardous chemicals

“Persistent organic pollutants” Characteristics: persistence in

environment (air, soil, water); bioaccumulate (fish, marine mammals); toxic

Category of “POPs” is a science-policy hybrid

Subject to international agreements (global Stockholm Convention)

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What are POPs and why are they a problem?

Pesticides, e.g. DDT, Chlordane: carcinogenic, ecotoxic

Subject to international regulation because of long-range transport

Accumulation in the Arctic, in traditional foods, far from location of use/release

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How to determine whether a chemical is a POP?

Data requirements for persistence, bioaccumulation

“Environmental fate properties and/or model results that demonstrate that the chemical has a potential for long-range environmental transport…” [Stockholm Convention]

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Stockholm Convention and additional POPs

The 2001 Stockholm Convention initially dealt with only 12 persistent organic pollutants (POPs)

It included a procedure for adding future substances to the agreement, based on scientific criteria of persistence, bioaccumulation, toxicity

10 additional substances have so far gone through the process

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Adding POPs to the Stockholm Convention: 5-step review process

Party submits a proposal to regulate a new chemical based on information requirement in Annex D (Persistence, bioaccumulation, toxicity info)

POPs Review Committee (POPRC): 31 government-designated experts decides whether criteria met

Soliciting of technical comments, development of risk profile by POPRC

Soliciting of comments, POPRC develops risk management evaluation and submits to the Conference of Parties (COP)

Conference of Parties takes final decision on whether to list chemical and where

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Review Committee Issues

Composition: regional, disciplinary Language Procedure and timing (meeting

frequency) Capacity (for proposing, and

analyzing)

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INTERNATIONAL CRITERIA FOR POPs Bioaccumulation: Bio-accumulation factor (aquatic) > 5000 or log Kow > 5, OR Evidence of high bioaccumulation in other species, high (eco)toxicity, OR Monitoring data in biota Persistence: Half-life of 2 months in water, or 6 months in soil, or 6 months in sediment, OR Evidence of sufficient persistence to justify consideration Long-range transport potential: Measured levels in locations far from releases, OR Monitoring showing long-range environmental transport may have occurred, OR Environmental fate properties or model results showing potential for transport Air half-life > 2 days for chemicals transporting through air Adverse effects

Criterion Stockholm CLRTAP Bioaccumulation Log Kow 5 5

Bioaccumulation Factor 5000 5000 Persistence Water 2 months 2 months

Soil 6 months 6 months Sediment 6 months 6 months

Transport Air 2 days 2 days

Log Kow=octanol-water partition coefficient, measure of lipophilicity Bioaccumulation factor: takes into account environmental and dietary sources

[Eckley, Environment, 2001; Rodan et al., ES&T, 1999] 20

SETTING CRITERIA: WHERE ARE THE DIRTY DOZEN?

[Rodan et al., ES&T, 1998]

Stockholm POPs Additional CLRTAP POPs Other chemicals

[Rodan et al., ES&T, 1999]

© American Chemical Society. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/.Source: Figure 2 in Rodan, Bruce D., David W. Pennington, et al. "Screening for Persistent OrganicPollutants: Techniques to Provide a Scientific Basis for POPs Criteria in International Negotiations."Environmental Science & Technology 33, no. 20 (1999): 3482-8. 21

Example review process: Lindane

Proposed by Mexico, June 2005 Lindane=gamma-

hexachlorocyclohexane Agricultural insecticide, treatment of

head lice Measured in the Arctic; toxic to rats;

carcinogenic in mice; accumulates in humans

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Procedure (Lindane example) 6/05: proposal by Mexico 11/05: POPRC says satisfies screening criteria 11/06: POPRC adopts risk profile 11/07: POPRC adopts risk management

evaluation 5/09: COP includes Lindane on Annex A

(Elimination), with specific time-limited exemptions for some head lice use

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LRTP vs Pov

LRTP=long-range transport potential

Pov=overall persistence

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Transport distance v. overall model persistence

Other approaches to identify POPs: Model overall environmental

persistence (sometimes, different results from half-life approach, see Klasmeier et al. 2006)

Screening based on quantitative structure-property relationships (Muir and Howard, 2006 identified 30 with bioconcentration potential and 28 with transport potential)

But, challenges in monitoring and measurement exist.

[Rodan et al., ES&T, 1999]

© American Chemical Society. All rights reserved. This content is excludedfrom our Creative Commons license. For more information, seehttp://ocw.mit.edu/help/faq-fair-use/.Source: Figure 2 in Rodan, Bruce D., David W. Pennington, et al. "Screeningfor Persistent Organic Pollutants: Techniques to Provide a Scientific Basis forPOPs Criteria in International Negotiations." Environmental Science & Technology33, no. 20 (1999): 3482-8.

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Long-range transport potential Characteristic travel distance (unit:km): the

distance at which concentration has decreased to 37% assuming constant flow of air

Air speed: 4 m/s, Water speed: 0.02 m/s Calculated for release to water and air Decrease in concentration from degradation,

transfer

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Scheringer et al., http://www.sust-chem.ethz.ch/docs/POP_Candidates_OECD_Tool.pdf

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Figure of characteristic travel distance (CTD) removed due to copyright restrictions. Please

see figure 2 in Scheringer et al. (2006) at http://www.sust-chem.ethz.ch/downloads.

Scheringer et al., http://www.sust-chem.ethz.ch/docs/POP_Candidates_OECD_Tool.pdf

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Figure of transfer efficiency (TE) removed due to copyright restrictions. Please see

figure 2 in Scheringer et al. (2006) at http://www.sust-chem.ethz.ch/downloads.

Chemical property inputs

Kaw=air water partition coefficient; related to Henry’s Law (which deals with pressures not concentration). [air]=[water]*Kaw

Kow=octanol-water partition coefficient. Measure of lipid solubility.

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Table of chemical properties used as input for calculations with the tool removed due to copyright restrictions.Please see table 1 in Scheringer et al. (2006) at http://www.sust-chem.ethz.ch/downloads.

Screening Tool Results

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Figure of "Results from the Tool for the four POP candidates and 10 generic PCB homologues in comparison" removed due

to copyright restrictions. Please see figure 4 in Scheringer et al. (2006) at http://www.sust-chem.ethz.ch/downloads.

Uncertainty

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Figure of "Results from a Monte Carlo calculation for gamma-HCH." removed due to copyright restrictions.Please see figure 6 in Scheringer et al. (2006) at http://www.sust-chem.ethz.ch/downloads.

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ESD.864 / 12.844J Modeling and Assessment for PolicySpring 2013

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